This invention relates to activated carbon fabrics.
Carbon fabrics are conventionally made from cellulose fibres or from polyacrylonitrile fibres or from pitch-based fibres. Cellulose fibres are commonly used where activated fabrics are required, though the process of activation, which involves heating for more or less extended periods at elevated temperatures, causes substantial loss of strength. Various impregnants such as Lewis acids or phosphorous compounds have been used to reduce the loss of strength somewhat. Nevertheless, activated carbonised cellulosic fibres are commonly used in composite structures such as laminated or quilted fabrics or in wrapped e.g. cotton-wrapped yarns, or knitted or woven together with supporting yarns, principally on account of their low strength.
Precursor fibres derived from polyacrylonitriles, however, are not, or not so readily, activatable under conditions for activating cellulose based fibres. Heating at the same elevated temperatures and for similar periods as are required for the activation of cellulose-based fibres does not adversely affect the strength of the acrylonitrile-based fibres to the same extent.
Because, particularly, of the lack of strength of cellulose based activated carbonised fibres, it is much preferred that, rather than fabricate fabrics from carbonised yarn or fibre the uncarbonised yarn or fibre is first fabricated and then carbonised in fabric form. Even so, however, higher levels of activation, where the fibre is capable of absorbing more molecules, are substantially precluded on account of the considerable loss of strength involved in attaining those higher levels through prolonged elevated temperatures.